The hardest one for me is the Qi fruit one. I've tried it many times and never got enough fruit! I have never tried the Skull Cavern one, because the regular Skull Cavern is hard enough. I can do the 50 loved gifts and the ship $100,000 worth of fresh cooked goods and the red, blue, green, etc., but that's about it!
I tried and failed hard on my first Qi Fruit. But I got it on the second, here's how:
1) get it early in the month, you have 27 days if you get the quest on day 1 but only 13 days if you get it on the 15th
2) Amplify your Qi Bean output by immediately running your early Qi Fruit through Seed Makers until you have about 150-200 planted
You'll be looking for Beans everywhere, I found the Volcano and Mines to be good sources. I dedicated about 200 spaces and about 6 Seed Makers on Ginger to the project but ended up using maybe 170 spaces before I calculated I had enough. I got the Quest on the 4th of the Month so I only lost about 1 round of growing and Seed Making.
But.
It's not worth it. Wayyyyyyyyy waywaywayyyayayayyayayayayay too much work!
Just do the Prismatic Grange, I did it like 5 times over with just what I had sitting in chests and now my Horse follows me everywhere!